This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. HS functions as a co-receptor by interacting with ligands alone or with both ligands and receptors. These modes of interaction are shared by a variety of growth factors, morphogens and extracellular matrix (ECM) proteins. Biochemical studies using oligosaccharides have established that, in general, HS requires distinct structures to interact with different proteins. However, the structure-function relationship of HS in its role as a co-receptor in a cellular context is far more complex. This in part results from the fact that natural HS is much larger than the oligosaccharides used in biochemical analyses, may interact simultaneously with both ligand and its receptor via distinct binding sites, and may also harbor multiple copies of the binding sites. Here we aim to develop cell-based assays to extend and to validate biochemical findings in a cellular context for a better understanding of the biological functions of HS. In particular, we are utilizing our generated serial HS mutant mouse lung endothelial cells (MLEC) as the model system to develop cell-based assays to determine the general role and the structure-function relationship of HS co-receptor functions.